The invention relates to a ventilation arrangement for a fuel tank of a vehicle.
During the course of the drive development of motor vehicles, vehicles are being developed which, besides the classic combustion engine, also include a drive that is electromotorically fed by a battery. These vehicles are also called hybrid vehicles and make possible locomotion for a certain time solely with the help of an electric motor.
The fuel required for operating the combustion engine is stored in a fuel tank, from which with the engine stationary, vapors escape because of vapor pressure differentials relative to the surrounding atmosphere, which are conducted through an activated charcoal filter inserted in a ventilation line, which is intended to adsorptively bind hydrocarbon components. With the engine running, by contrast, these retained hydrocarbon components are absorbed by inflowing air and fed to the combustion engine process of the engine, so that their escape into the environment is likewise prevented.
Since in the time of an exclusively electric operation of the vehicle, no ambient air flows through the activated charcoal filter, a regenerating of stored hydrocarbon components is not required during this time. In order to achieve an at least approximately regeneration despite the thus reduced operating time of the combustion engine, a pressure that is increased compared with the surrounding atmosphere is demanded in the head space of the fuel tank in order to reduce the amount of hydrocarbon components that have to be adsorbed in the activated charcoal filter.
It is generally known, to limit the pressure in the head space of the fuel tank by means of a pressure relief valve for safety reasons. This pressure relief valve establishes a continuous connection between the head space and the surrounding atmosphere when an overpressure or a maximum pressure occurs.
It is known, furthermore, to limit the pressure drop within the tank during the operation of the combustion engine as a result of a continuous removal of fuel through a valve, which on undershooting a minimum pressure, establishes a connection to the surrounding atmosphere and thus a pressure balance.
While refueling the vehicle, the gas volume displaced by the inflowing, liquid fuel plus fuel evaporations have to be conducted out of the tank. In the process, a pressure balance with the surroundings has to be established through a complete ventilation, since otherwise fuel is discharged from the filler tube of the tank.
However, this demand opposes the desire for an increased pressure in the fuel tank.
For operating a fuel tank in which an increased internal pressure has to be maintained, there is thus the necessity of three valves. These have to have an adequate tightness, since otherwise the pressure forming in the tank would be removed with prolonged stoppage and the conditions mentioned at the outset of a quantatively balanced adsorption and desorption of hydrocarbon components in the activated charcoal filter could not be satisfied.
From the associated main application 10 2010 044 336.0, a ventilation arrangement for a fuel tank of a vehicle is known, wherein in a housing the functions of a pressure relief valve, of a valve for ventilation for the purpose of limiting a negative pressure during the operation of the motor and that of an electromagnetically switchable valve, which is intended for producing a pressure balance with the surroundings during refueling, are combined.
For establishing preferably low flow resistances, the line cross sections, via which the ventilation arrangement is in connection with an activated charcoal filter and the head space of the tank, is dimensioned relatively large. However, this in turn results in high actuating forces even with low pressure gradients, which have to be created via the drive of the electromagnetically switchable valve. Usually, a magnetic drive or an electric motor is employed at this point, which however in view of the switching forces to be created, have to be dimensioned relatively large. The dimensioning is accompanied by a correspondingly large volume.